The mechanical response and microstructural evolution of 2195 Al–Li alloy during hot tensile deformation

Abstract

Hot tensile deformation behavior of 2195 Al–Li alloy was investigated at the temperature of 420–520 °C and the strain rates of 0.01–1 s−1. The mechanical characteristics and microstructural mechanism were discussed. Overall, the tensile strength increased with decreasing temperature and increasing strain rate, and the total elongation was more sensitive to temperature than to strain rate. At each strain rate, the elongation firstly increased and then decreased with the rise of temperature and it showed the maximum at 440 °C. Particularly, the fracture mode gradually changed from ductile fracture with dimples to brittle fracture with cleavage steps when the temperature exceeded 440 °C at each strain rate. This was attributed to the larger proportion of coarsening grains with a diameter exceeding 15 μm. The total elongation (E) showed a linear relationship with the proportion of coarsening grain (P). The larger the P was, the lower the E was. EBSD results showed that although the dynamic recrystallization (DRX) level, facilitating to improvement of ductility, increased with the rising of temperature, the recrystallized grains became larger at higher temperatures due to rapid growth rate, especially at lower strain rate, then a decline of the total elongation displayed. Moreover, a large number of fine precipitations of θ′ and δ′ phases distributed dispersedly in the matrix at the deformation temperature of 440 °C. However, the overall number of the precipitations decreased when the deformation temperature further increased. The θ′ phase completely dissolved into the matrix, only a small amount of δ′ phases could be observed at 480 °C and 500 °C, thus the pinning effects on the grain boundary migration were weakened, whereby the grain size displayed an additional increase.